Deleting the application would be pretty hard to do. It may be that you've just removed the icon from your dock. To see if this is the case, go to the Apple Menu and the 3rd item should be "App Store..."
If that works, all you need to do is open the store from there. To get the icon back on your dock, right click on it when the app store is open and choose Options -> Keep In Dock.
Yes, I figured out that I need to reinstall the system. (Either the combo or from the disks I already have). I hoped for a more simple/faster solution, like reinstalling just the App Store.
And yes, indeed I deleted the App, not just the icon from the Dock. It's a long story...